An Assessment of Future Caribbean Climate Changes using the BAU Scenario by Coupling a Global Circulation Model with a Regional Model

The Global average CO2 mixing ratio has been increasing since the end of the XIX century mostly due to the burning of fossil fuels and has been correlated to increases in surface air temperature, variations in precipitation patterns, among other climatic variables. The Small Island Developing States, according to the 2001 Report of the Intergovernmental Panel on Climate Change (IPCC), are likely to be among the most seriously impacted land areas by global climate changes. In this work, the Parallel Climate Model (PCM) and the Regional Atmospheric Model System (RAMS) are used to investigate the impact of future global anthropogenic CO2 concentration increases over the Caribbean region. RAMS was coupled with PCM to predict climate changes in 2048 under the Business as Usual Scenario of the IPCC. To reach these goals, the Caribbean rainfall season is divided in the Early Rainfall Season (ERS) and the Late Rainfall Season (LRS). To carry out the climatological Caribbean season analysis, the National Center for Environmental Prediction reanalysis data, the Xie-Arkin rainfall data and the Reynolds-Smith Sea Surface Temperature (SST) data were used. PCM is first evaluated to determine its ability to predict the Caribbean climatology. As a result, PCM tends to slightly under predict the Caribbean SSTs, which along a cold advection cause a lower rain production than the observed climatology. Future predictions indicate that the rainfall annual variability simulated by PCM from 1996 to 2098 is affected by feedback processes and by the synoptic indices SOI and NAO. The future Caribbean climatological condition (from 2041 to 2055) simulated by PCM shows a future warming (SSTs) of up to approximately 1 deg. Celsius along with an increase of the rain production during the Caribbean seasons. Although the vertical wind shear is strengthened, it continues to produce values lower than 8m/s which allow a more intense rainfall in the ERS and LRS. The vertical wind shear below 8 m/s and the warmer Main Development Region Sea are optimal conditions to possible increases in tropical storms frequency in the future. Results from the dynamic downscaling of PCM by the use of mesoscale model RAMS indicate that the climate change between the control year of 1998 and the future of 2048 reflects an average increase in air temperature of 1.5 deg. Celsius for the Caribbean region which results in an average precipitation increase of 20 mm. In a similar response as the PCM, the mesoscale rainfall production is driven by the vertical wind shear below 8 m/s and the dry/moisture advection, especially in the Caribbean late rainfall season. The RAMS finer grid predicts a future warming of the Island of Puerto Rico of up to 2 deg. Celsius along with a wetter 2048 island of Puerto Rico than 1998 with a future increase between 15 and 30 mm.